Administration of intravenous fluids to a patient is well known in the art. Typically, a solution such as saline, glucose or electrolyte in a glass or flexible container is fed to a patient's venous access site via a length of flexible plastic tubing such as polyvinyl chloride (PVC) tubing. The rate of flow of the fluid is controlled by a roller clamp which is adjusted to restrict the flow lumen of the tubing until the desired flow rate is obtained.
Flow from the container to the patient may also be regulated by means other than a roller clamp. It is becoming more and more common to use an electronically controlled pump. One type of pump that is used for intravenous fluid administration is a peristaltic-type pump.
Use of peristaltic pumping action is particularly well suited for the medical field. This is because peristaltic pumping action can be applied externally of the tubing carrying the intravenous fluid. This maintains the sterile condition of the intravenous fluid within the tubing while imparting fluid propulsion on the fluid. The peristaltic pumping action can also be applied at any point on the tubing.
In a common type of peristaltic pump used in the medical field, a driving motor is connected to an array of cams angularly spaced from each other. The cams in turn drive cam followers which are connected to corresponding pressure fingers. These elements cooperate to impart a linear wave motion on the pressure fingers. A pressure plate is secured juxtaposed to and spaced from the pressure fingers. The pressure plate holds the tubing against the reciprocating pressure fingers to impart the wave motion on the tubing to propel the fluid. Alternatively, the driving motor drives a rotary-type peristaltic pump in which a plurality of rollers contact the tubing to impart fluid propulsion. A pressure plate holds the tubing adjacent to the rollers.
In a preferred embodiment of peristaltic pumps, the driving motor is a stepping motor which rotates in small increments or steps. While a stepping motor rotating at a high rate of speed gives a visual impression that the rotation is constant, the stepping motor in fact turns through a series of small angular increments or steps which are followed by a brief period of rest. In stepping motors utilized in peristaltic pumps in the medical field, these small angular steps can range from about 0.36.degree. to 7.2.degree. and in a preferred embodiment are about 1.8.degree.. This results in a series of steps of the shaft between 1000 and 50 per revolution or, in the preferred embodiment, about 200 steps per revolution.
Accurate monitoring of the pumping action of such a peristaltic pump is desirable in a number of areas. For example, peristaltic pumps in the art have the potential for slippage during the pumping period. Slippage occurs when excessive torque requirements are placed on the driving motor so that rotational movement does not occur even though power is being applied to the motor. Slippage can be caused by, for example, motor friction, tubing variances and peak torque requirements, which can vary greatly during a peristaltic pumping cycle. If slippage is detected, it can be solved by adjusting power supplied to the motor to compensate for the torque variation.
Another area in which accurate monitoring of the pumping action is desirable is in the measurement of the length of time and number of rotations that the pump incurs. This is important to determine flow rates as well as to detect excessive occlusion pressures and air embolisms.
Still another area in which accurate monitoring is important is in monitoring the direction and rotation of the pump. Peristaltic pumps which are driven by stepping motors can move in an abnormal direction as a result of, for example, improper application of the driving pulse sequence due to parts failure or the application of a different pulse width or frequency modulation sequence to drive the motor. When such abnormal operation occurs, it is desirable to signal such abnormal operation so correction can be made or to correct such abnormal operation by adjusting the pulse sequence.
What would thus be desirable would be a peristaltic pump which could efficiently monitor the operation of the pumping action, signal power adjustment when slippage occurs, prevent abnormal motor rotation and improve accuracy by detecting rotation in small sector increments. This system also should be economical and reliable. The present invention provides such a device.